PPQS Flashcards
Suggest whteher clf3 HAS polar bonds
YES
- F more electronegative
- d+ cl, d- f
electronegativity
ability of an atom to attract the electronS in a covalent bond
why do repeats?
- increase repeatability
- find anomalies AND DISCARD
atomic emission spectra provisde evidence for …
quantum shells
6 MARKS
Problems and improvements of collection over water(gas collected 2 low)
- gas escapes from apparatus. use airtight bung with gas syringe
- metal covered with an oxide. clean with abrasive BEFORE weighing
- mass of metal used too low. use a more PRECISE balance
shortest bond length in CH3OH
O-H as largest difference in electronegativity
hydrogen bond angle
ALWAYS 180
- 2 bonding pairs
- 0 lone pairs
trigonal bipyrmaidal angles
- 5 bp, 0 lp
- 90 and 120
explain why the positive charge is on the carbon atom shown
tertairy carbocation is more stable than a primary carbocation
because it has more positive inductive alkyl groups
importance of termination (2)
- 2 free radicals join together
- dont form any free radicals
describe what is meant by cracking (2)
- use of high temperatures
- to break large molcules into smaller molecules, ,and produce alkenes
why can propene form 2 possible products with HBr
- asymmetric alkene
- Br could join to c1 or c2
- to form 1 bromo or 2 bromo propane
biggest hazard of alkanes
flamable
in combustion where must the u-tube go
BEFORE boiling tube w lime water; distinguishes water as a product of combustion rather than the limewater
why can hydrogen chloride gas not conduct electricity but HCl acid can
covalent bond in hydrogen chloride changes to an ionic bond in aqueous solution
pressure in pvnrt is in
PASCALS
EXPLAIN WHY METHANOL IS SOLUBLE IN WATER
- hydrogen bonding between them both
- of same strength
- comparable to the strength of the bonding in either component on its own
why is NaCL soluble in water but not methanol
- hydration of BOTH ions in water
- but ionic bonding is stronger than bonding between ions and methanol
2 reasons why x is more electronegative
- more protons
- smaller atomic radius
despit ehaving polar bonds why is x not polar
- symmetricak
- BOND POLARITIES CANCEL
use mexwell boltzmann diagram to explain why the use of a catalyst increases the rate of decomposition of ammonia (3)
- area under curve represents fraction of molecules with E>= Ea
- area with Ea of catalyst is greater; more molecules have E>= Ea
- more freqeunt successful collision
similarities (2) and differences (2) between pi and sigma bonds
SIMILARITIES:
- both include the overlap of orbitals
- both involve electrostatic attraction between a BONDING pair of electrons and positive nuclei
DIFFERENCES:
- pi = sideways overlap of orbitals
- sigma = direct end on overlap of atomic orbitals
explain maxwell boltzmann at high temp
- peak shifts to the right and lower
- at higher temperatures there are more particles with higher energy
why might reaction not happen as shown
- might react with oxygen
- unlikely for reactants to be in correct ratio
- reaction must occur in a series of steps as too many particles reacting in equation
+- of chemical test vs infrared to show alcohol
+
cheaper
rapid
can be done in schools
-
CHEMICAL TEST NOT AS SENSITIVE
vol gas a bit higher at higher temp
gases expand when heated
why is the measurement of initial rate less accurate than max
- difficult to judge where tangent should be drawn for 0
- compared to other points on the line
why is a heterogeneous catalyst good for gas reactant
provides a surface for the reaction
why might uncertainty of someone else be hgiher with mass measurement
they used a smaller mass w same balance
why does catalyst not effect amount of product made
increases rate of forward and backward reactions
why is catalyst heated and why might it melt
- heated to provide activation energy
- metls as bonds broken
advatnage of catalyst iN INDUSTRY
- decreases activation energy
- allows milder conditions to be used (lowering cost)
chromate (VI) ion colour
YELLOW
WHY IS ice less dense than water
- water molecules in a lattice
- molecules further apart in ice than water
TMS purpose
reference peak to compare other shifts to
what does NMR actually do
change spin state of hydrogen nuckeus
effect of increasing temp on rate constant
increases
why is there at least 2 steps (RDS REFERENCE)
- x and y in RDS (z not in)
- but more reactants in full equation
- so must be another step containing z
why is the major product from the tertiary carbocation
- most stable
- inductive effect of alkyl groups
why are the other reactant concnetrations in hUGE excess in iodine clock reaction
- concentration remain constant
- so that [I2] is limiting reagent; only its concnetration changes
-OTHERWISE A CURVE IS OBTAINED AS FULL ORDER OF REACTION
how to measure order of propanone as 1st order after already doing one step of iodine
- doulbe conc of propanone
- rate should double (gradient doubkes)
OR - measure conc propanone over time
-constant half life
how to quench iodine TITRATION
- add NAHCO3
- neutralizes acid
sodium hydrogencarbonate neutralising ACID catalyst ionic equation
HCO3- + H+ = H2O + CO2
why is mols of soidum thiosulfate v low
- so concentration of reactants doesnt fall significantly before end point reached
- used up during initial rate period
quenching with IODINE CLOCK method
- take samples at various times
- quench with ice
- titrate using alkali
why might u get anomalies where rate is too high
- rate is too high
- reaction exothermic
- more collisions with E>= Ea
what happens if no thiosulfate added in iodine clock
reaction goes blue black immediately
purpose of thiosulfate
- as soon as iodide reacts to form iodine, thio reacts to turns it back to iodide
- to prevents colour change occuring until a set amuont of reaction occured
how to use colorimetry for iodoine(3)
- colorimetry
- measure absorbance
- CALIBRATION CURVE to turn it into concentration. absorbance proprotional to concentration
biggest alkane hazard
TOXIC BY INHALATION
reforming defition
converting straight chain HC to a ring/branched
cracking defintion
breaking a longer HC to shorter chain HC
describe waht happens to pi and sigma bonds in addition
- pi bond breaks
- sigma bond remains
- as pi weaker
- forms a carbocation intermediate
alkene with acidificed potassium manganate (7)
DILUTE SULFURIC ACID
- forms a DIOL
- purple to colourless
a fuel is …
a substance that produces energy
why might the fuels be liquified
easier to transport
hazard vs risk
hazard: potential to do harm
risk: likelihood harm will result
which o the 2 ions has POLARIZING ability
cation
formation of acid rain rain on limestone
REACTS with limestone to corrode buildings
why conducgtivity different (ionic compounds)
cations are diff sizes
why cant silicon conduct electricity
- outer electorns FIXED in covalent bonds
- no delocalised electrons
why are polymers not sustainable
made from crude oil which is non-reneweable
why is pi weaker than sigma
- sigma direct end on overlap of orbitas- along line in between the 2 nuclei
- pi = sideways overlap
why is ice less dense than water
- molecules spread out further apart
- in a lattice
- h bonds longer than covalent bonds
why non polar insoluble n water
cant h bond with water
ionic compounds solubility
- soluble in water, ions hydrated
- enthalpy change of hydration compensates for energy needed to break part lattice
- INSOLUBE in non polar as any forces that would form between ion and substance weaker than ionic bondng
describe the structure of. metal (3)
- lattice
- positive metal cations in layer
- sea of delocalised electrons
electrolyss of CuCrO4
- ions migrate
- Cu2+ blue colour towards cathode
- CrO4 2- yellow colour towards anode
2 sources of repulsion in ionic lattice
- ions of same charge repel
- positive nuclei repel
purpose of reforming
- more efficient combustion
- fuels with a higher octane number
- NO KNOCKING
why might volume co2 be slightly lower
- sligthyl soluble in water
using a smaller cylinder multiple times vs a bigger one once
- look at error/ncertainty
- more time taken to refill loads
- GREATER TRANSFER LOSSES
why does distillation work
- difference in bp
- the one with lower bp boils and vaporises first, so can be condensed and then collected
purpose of reflux
- reactants vapourise, then condense
- return to reaction mixture
- allows to reach BP without LOSS OF REACTANT
HOW TO DISTILLATE TO GET PURE PRODUCT
- heat
- collect distillate
- at BP of the prducrt
c-c with bromine vs c=c
- c-c sigma only
- strong bond, need to break c-h aswell
- c=c sigma and pi
- e- desnity above and below plane, polarises br-br
- pi bond weaker so easier to break
2 conditions for cracking
- high temp
- silica catalyst
conditions for haloalkane and ammonia and why
- heat in a sealed vessel
- increases pressure to increase rate of reaction]
- but prevents loss of product
purpose of needing ethanol with the water and AgNO3 for haloalkane test
- cosolvent
- dissolves both haloalkane AND water
BP 2 chloro 2 methyl propane
50-52
rate of hydrolysis primary, secondary, tertiary
primary slowest
orbital
- a region where there is a high probaility of finding electrons
- holds up to 2 electrons with opposite spins
explain why 1st electron affinity is negative but second is positive
- negative as exothermic due to attraction between POSTIIVE nucleus and electron
- postivie as endothermic as energy required to overcome
- repulsion between negative ion and electron
assumptions for theoretiacl lattice energy (2)
- 100% ionic bonding
- ions are perfect spheres
final comment for the theoretical lattice energy questions
- more energy released when making the bond, so bond is stronger, and LE more exothermic
2 problems with free radical substitution
- cant control number of cl that will substiutte; oversubstitution
- mixture of products will form, need to separate
) Explain why benzene is resistant to bromination but ethene reacts readily
with bromine at room temperature.
- ethene c=c, electron density localised
- electron density delocalised in pi structure of benzene
- high ea for benzene as energy needed to break structure
- ethene more susceptible to electrophilic attack
length hydrogen bonds compared to covalent
LONGER
BIGGEST DIFFERENCE BETWEEN ACID HYDROLYSIS OF ESTER AND ALKALI
acid: acid is catalyst
alkali: alkali is a REACTANT
why are condensation polymers biodegradable
ESTSER link can be hydrolysed by enzymes
temperature conditions for nitration of benzene and why
- below 55
- PREVENTS MULTIPLE SUBSTITUTIONS
Why is organic synthesis with less steps more eco frendly
higher yield
reaction to form no2 + for nitration of benzene
HNO3 + 2H2SO4 = 2HSO4- + NO2+ + H3O +
if Kp is x^2/y, discuss effect of incrasing pressure
- increases partial pressure of numerator more than denominator as squared
- so the mole fraction of y increases
- to resotre Kp
why hard to measure temp endo
difficult to measure temperature whilst heating
describe what happens when copper sulfate dissolves in water
- ionic lattice broken
- water hydrates each ion
why is HF boiling point the most
- F is MOST ELECTRONEGATIVE ELEMENT
- So stronger hydrogen bond
2 problems with NOx that arent ghg
- dissolve in water to form acid rain
- breathing problems
bond angle ice and water
different
eg Kc is 1
there are more moles of products than reactants explain
- calculat new Kc; Kc >1
- moles products must decrease AND moles reactants must increase to restore Kc
- POE shifts to the left
test for halide
HNO3
AgNO3
WHAT SHAPE IS CATALYTIC CONVERTER AND WHY
- honeycomb
- increases SA
- allows gases to flow through
why cant distillation make ethanioc acid
- ethanol oxidised to ethanal
- low bp, distilled of as soon as formed
- before full oxidation to ethanoic acid
why would rate of reaction with oxygen decrease in a sealed vessel
concentration of oxygen decreases
ratio of 35 Cl 2 , 35Cl37Cl, 37Cl2
9:6:1
which apparatus for oxidation to ketone
- reflux
- to ensue full oxidation
why might a temperature reading be wrong
- mixture not stirred so temperature not unifor
who burns wiwth a sooty flame
greater c:h
eg alkenes
what does having a methyl group on the benzene ring do
INCREASE electron density
- positive inductive effect
if organic synthesis q, increase carbon chain how?
- if x1 : CN
- if loads: polymer
- if by a specific number of C : GRIGNARD
in complete oxidation the oxidising agent is
in excess
why might you get Cl 36 in mass spec
[35Cl37Cl]2+
m/z 36
steps of recrytallisation
- dissolve impure in MINIMUM volume of hot solvent
- filter it hot through a preheated funnel
- cool in ice bath + stir with glass rod
- vaccum filtration (buchner filtration)
- RINSE WITH ICE COLD ETHANOL
- dry between filter paper
distillation vs separating funnel
distillation: difference in BOILING POINTS
separating funnel: immiscible liquids
if one H+ is used in the reaction but 2 are produced, can it still be a catalyst?
YES
- One is regenerated, so thats the catalyst
- one is a product of the reaction
recrystallisation: why cool in ice bath
- product is less soluble in colder solutions so will crystallise out
recrystallisation: why warm filtering
- to prevent crystallisation
- which would reduce yeild
recrystallisation: why buchner filtration
- removes remaining solution (soluble impuirities) faster
- dryer crystals
problem if you have impurities in a gaseous reaction with a heterogeneous catalyst (3)
- impurities ADSORB onto surface of catalyst, occupying active sites
- fewer active sites avilable for reactants to adsorb
- IMPURITIES LESS LIKELY TO DESORB
purpose of TMS
- calibration
- to compare other hydrogen shifts
explain why you can get pcl5 but not ncl5
- PCl 5 can expand its octet
- NCl5 cannot as no d orbital
